Natural Gas Preservation Conditions Of Changxing-Feixianguan Formation In Micang Mountain Front And Its Margin

The exploration of hydrocarbon resources in complex piedmont zone is a difficult geology problem faced by scholars at home and abroad.The frontal zone of Micang mountain and its peripheral areas lie in the northeast of Sichuan province,where the marine carbonate formation underwent multi-stage tectonic movements,therefore the preservation conditions of oil-gas reservoirs become the main constraints of hydrocarbon accumulation in Changxing and Feixianguan Formation of that region.Based on the theory of basin fluid chemistry-kinetics and oil-gas preservation unit,holding the principle of combining the study of surface geology and subsurface geology,we establish the structural framework of mountain front of Micang mountain and its margin,comprehensively evaluate natural gas preservation conditions of Changxing and Feixianguan Formation and recognize the favorable exploration zones.Main achievements are as follows:?1?The tectonic zones are,from Micang mountain core to basin,thrust belt,fault-fold zone,concealed fault-fold zone and fold belt;structural styles mainly involve fault-related fold,wedge-shaped duplex,thrust triangle structure and pop up structure.?2?The variation in thickness of halite cap rock,which overlies objective intervals in the study area,is controlled by the thrust fault;The thickness of gypsum-salt rock and its buried depth together determine its sealing capability.?3?we calculate the?Na⁺/?Cl^-,?SO₄^2-×100/?Cl^-and the salinity,then divide the target zones into three hydrogeological divisions:free exchanging zone,exchanging-retarded zone and exchanging-stagnant zone by establishing evaluation standard of preservation conditions.?4?The fault-fold zone of study area is divided into free exchanging zone;The concealed fault-fold zone is divided into two different hydrological systems:the northern region belongs to free exchanging zone and the eastern region of Tongnanba anticline belongs to exchanging-retarded zone;Fold belt is divided into exchanging-stagnant zone as a whole.?5?Tongnanba anticline,including Hebachang and the concealed fault-fold zone,is favorable gas accumulation and preservation zone.